1. Field of the Invention
The invention relates to a manufacturing process for forming an optical fiber, and more particularly to a system that is used in the drawing process of producing optical fibers to prevent polarization mode dispersion.
2. Description of the Related Art
In general, an optical fiber manufacturing process involves a process of preparing an optical fiber preform, and a process of drawing an optical fiber from the prepared optical fiber preform. In such a drawing process, a standing drawing tower is used which heats, melts, and draws an optical fiber preform to produce an optical fiber.
U.S. Pat. No. 5,298,047 entitled, “Method of Making a Fiber Having Low Polarization Mode Dispersion due to a Permanent Spin” and U.S. Pat. No. 6,076,376 entitled “Method of Making an Optical Fiber Having an Imparted Twist”, disclose an arrangement for applying a spin to an optical fiber that is drawn during the fiber operation, so that an optical fiber can be rolled by the swing motion of a swing guide roller.
FIG. 1 shows a conventional draw tower that is used to draw an optical preform to produce an optical fiber. As shown in FIG. 1, the fiber drawing process is vertically arranged in sequence into different steps within the draw tower. Initially, an optical fiber preform P is melted at a sufficient temperature, at least about 2000° C., in the furnace, then drawn about the central axis of the draw tower 100. The diameter of the drawn optical fiber F is controlled using a diameter regulator (not shown) and then cooled to a temperature that is suitable for coating the optical fiber via a cooling unit 4. The cooled optical fiber is coated while passing through a coater 6. Here, the coater 6 can includes a first coater and a second coater. The coated optical fiber passes through a number of ultraviolet curing apparatus (not shown) where the ultraviolet curing polymer coated on the optical fiber is cured. The ultraviolet cured optical fiber F is twisted using a pair of rollers 8 that is canted by an angle θ, and its polarization effect is suppressed. Thereafter, the optical fiber passes a capstan 10 and through a number of rollers to reach the winder 12 where the optical fiber is wound. The capstan 10 imparts a certain tensile force to the optical fiber preform so that the optical fiber can be drawn with a certain diameter size.
In the drawing process of the related art, the coated optical fiber directly contacts with the pair of rollers 8 and then twisted according to the canting motion of the rollers which helps to smooth the polarization mode dispersion of the optical fiber. However, the related art has the following problems: First, vibration in a transverse direction is incurred to the optical fiber due to a direct contact and high speed drawing operation, thereby causing it difficult to control the outer diameter of the optical fiber. Second, as the optical fiber contacts directly with the guide roller, the optical fiber can be weakened according to the surface state of the roller, and this can be fatal the optical fiber. Third, a precise control of coating the outer diameter is difficult as the optical fiber is periodically vibrated when the drawing speed is high. Also, in the case of wet-on-wet type coating, the high speed drawing that is stable is difficult to achieve as the first and second coating materials are mixed to cause coating instability.